One such belt is proposed in U.S. Pat. No. 4,047,446. In that patent, the ridges of the ribs are rounded so as to ensure gaps 52 and 53 of equal size firstly between the ridges 43 of projections 44 on the sheave and the bottoms 45 of the grooves 40 in the belt, and secondly between the ridges 50 of the ribs 35 on the belt and the bottoms 51 of the spaces between the projections 44 of the sheave, in order to avoid harmful contact between the belt and the sheave as the belt wears. That belt presents teeth of considerable height and it is very sensitive to bending/compression stresses.
In order to avoid the cracking that appears in the teeth of power transmission belts because of the stresses due to flexing back and forth, U.S. Pat. No. 4,904,232 proposes implementing teeth having ridges that present a circular profile, each ridge being made of an elastomer having hardness on the Shore A scale that is less than that of the remainder of the tooth.
Such a configuration suffers from the drawback of making belt considerably more complicated.
U.S. Pat. No. 5,803,855 proposes improving contact between the belt and the sheave by providing clearance spaces between adjacent ribs and by using non-linear contact surfaces so as to reduce stress concentrations at the ridges of the belt, and thereby reduce rib cracking. In that belt, the ridges may be circularly arcuate in shape and they connect with side faces that are not plane.
That type of belt is not easy to implement, in particular because of the non-plane profiles of the contacting surfaces which must be designed in such a manner as to ensure good power transmission and of the presence of clearance spaces between the ribs.
The present invention seeks to provide a belt that enables the cracking phenomena that appear at the ridges of the teeth to be avoided at least to a large extent, e.g. in motor vehicles (cars, motor bikes, . . . ).
Surprisingly, the Applicant company has found that the appearance of cracking in teeth ridges is liable to occur not only when the belt is subjected to flexing cycles.
Thus, the Applicant has found that there exists another phenomenon which has previously not been identified, constituted by the swelling of the free contact zone at the ridge of a tooth, which swelling is due to the tension in the belt and to the winding diameter, and it leads to deformation at the contact edges in particular, which can lead to the appearance of cracking. This phenomenon tends to predominate at small winding diameters (e.g. less than 60 millimeters (mm) as are to be found on alternator sheaves). Such small diameters are often present in the belt drive systems of cars.
U.S. Pat. No. 4,944,717 proposes mitigating the problem of flexing in flat-sided V belts by providing teeth with ridges that are concave in shape. However, such a profile is unfavorable from the point of view of swelling deformation since it induces a maximum additional amount of deformation at the ridges of the teeth.
Furthermore, suggestions have been made to trim the flat ridges of teeth as obtained by molding so as to rectify them by machining flat ridges that are connected to the side faces directly, or via small radii of curvature (0.6 mm or less). That makes it possible to eliminate the flat surface layer that comes from molding, which layer is the most fragile, but only at the cost of an additional rectification step. That profile is of reduced height and that makes it sensitive to the swelling deformation that is induced by establishing tension, since such deformation also depends on the winding diameter, thus giving rise to cracking appearing due to the swelling defect that had not been identified beforehand.
In other words, prior art solutions have led to an improvement in belt behavior faced with flexing phenomena, but that has generally been accompanied by deterioration in behavior faced with swelling deformation.
The object of the invention is to provide a belt that improves behavior relative to swelling that generates cracking at the ridges of the ribs.